I was able to modify the Wave SDK source code to work with 4.27, changing about 20 lines of C++ which caused the compilation to fail because of slightly changed function signatures on UE4.27's side. I haven't really tested it out yet, nor do I know if I can share the code based on the license, but what I did to find and correct these bugs are the following steps - I REPEAT ONCE AGAIN BARELY TESTED USE AT YOUR OWN RISK
1. Download the Wave zip, in the plugin (see lowercase) folder, find the file "plugin.uproject". Right click this in File Explorer and select "Switch Unreal Engine Version" (even if you only have 4.27), select 4.27 and click ok.
2. UE4 should generate project files. Double click on plugin.sln, open Visual Studio, and right click the plugin target in the solution explorer on "plugin" and select build.
3. VS should spit out a bunch of errors. The only things I recall that need tweaking is changing mentions to ->Resource to ->GetResource() and ->SetResource(), and accepting FRHICommandListImmediate& RHICmdList to a few function override signatures (also refer to UE4 source + intellisense).
4. If you fix these, it should build in VS, and therefore 4.27. Then (not sure if necessary) open plugin.uproject, and follow any additional instructions. The plugin in the Plugins folder should open in 4.27 compatible NOTE ONCE AGAIN BARELY TESTED USE AT YOUR OWN RISK